Important conditions affecting downhill skiers are the nature of the snow, the type of skiing to be done, the type of skis and bindings used and the skill of the skier. The snow and the ski run can vary during a day, while the ski and the skier are generally invariable. The snow can range from ice hard snow, to very loose or soft snow, sometimes called powder snow. There are profound differences in skiing turns and speed according to the type of snow being skied upon. One primary characteristic of a ski is its ability to bend or flex as it carries a skier. A ski flexes and counterflexes, and keeps the skier in control as he or she follows the contour of a slope and enables a skier to manipulate the skis as he or she bounds and rebounds down the slope. In racing events, the snow can be ice hard both to increase the skier's speed and to avoid ruts in the snow. Hard snow may limit the bending of the skis. Turning is mainly accomplished in hard snow by the skier tilting the skis to dig the edges at the bottom of the ski into the snow by shifting his or her weight and body position. On the other hand, the ski can bend a large amount in powder snow. The longitudinal sides of skis are convex arcs, and it is through the use of the side cuts and bending of the ski that the skier turns; the edges of the skis are of much less importance in turning in powder snow. Regular snow, that is snow whose texture and packing is between hard snow and powder snow, presents other problems to the skier. Experience, communications with racers and other skiing experts, and testing, indicate that a ski stiffer underfoot of the ski boot may be preferable in very hard snow conditions while an overall more flexible ski appears to be preferable in soft snow conditions. An intermediate situation is preferable for snow of intermediate softness. It is also known that a ski loosely attached to the skier transfers little energy from the ski to the skier when the ski encounters obstacles, thus resulting in higher speed. However, a loose attachment results in loss of ski control in turns; hence it is desirable to have a loosely connected ski when traveling essentially in a straight line for greater speed and a tightly connected ski when making turns for greater control.
The vibration characteristics of skis are also believed to be important. Skis have several vibration modes which are exhibited during skiing. High frequency vibrations break the contact between the ski bearing surface and the snow, which improves speed. On very hard snow conditions, the breaking of the contact between running surface and snow does not result in the same level of benefit but the ski still vibrates resulting in audible and perceptible chatter. A reduction in chatter is desirable in these conditions. Thus different requirements in underfoot stiffness and vibration exist depending on snow conditions. The ski designer, faced with the different kinds of snow, the different types of skiing, and variations in skiers and their bindings, can only develop skis which can handle all of these varying characteristics reasonably well but are not optimized for any specific condition.
All ski bindings have an effect on ski stiffness underfoot. When a ski bends during skiing, the distance between the toe piece and the heel piece varies since they move relative to each other with the upward curvature of the ski. However, the length of the ski boot sole remains constant. Therefore, there is generally a limited movement rearwardly of the heelpiece in a clamp on the ski to keep it in contact with the boot. The force required to move the heel unit back results in a stiffening of the ski section directly under the binding and boot. It is believed that most ski bindings on the market fall into this category. Therefore ski manufacturers take this stiffening action of the binding system into consideration in the design of the ski. The underfoot stiffness of the ski/binding combination is thus optimized for the type of skier and preferred snow conditions the ski was intended for. Different binding systems and separate devices to be used in conjunction with the ski and commercially available bindings have been manufactured to either increase or decrease the underfoot stiffness of the basic binding/ski configuration. Other devices can effect the normal vibration of a ski. Combinations which decrease stiffness underfoot may improve soft snow skiability while deteriorating skiability towards the end of the hard snow spectrum. Combinations which increase stiffness have the opposite effect.
In some systems, the binding is constructed to render the ski more flexible. In the ESS v.a.r. device, a boot support plate having a forward portion which is slidable in a channel on the ski, should render the ski more flexible. However, the support plate is fixed with additional fastening means to the ski, and thus is believed to limit its benefit on soft snow. The fixing of the support plate decreases the bending of the ski.
The Tyrolia Freeflex system utilizes a flexible plate attached to the top of the ski. The plate is fixed to the ski at the toe of the binding and is held in place about the heel by a slidable clamp fixed on the ski. Both toe and heel binding units are affixed on the boot support plate. When the ski bends, the heel clamp moves closer to the toe unit but the flexible plate is allowed to slide rearwardly reducing the tendency of the heel unit to move towards the toe unit as in a normal binding configuration. The ski is thus allowed to flex more underfoot. The plate is allowed to move in the slidable clamp but is also held to the ski by an additional sliding point between the toe and the heel. This mounting configuration increases sliding friction and thus the overall decrease of ski stiffening is relatively small. Devices of this nature are disclosed in U.S. Pat. No. 3,937,481.
Most ski binding manufacturers produce bindings which increase the stiffness of skis. The stiffness of a ski provides a firm edge to drive into the snow for making turns in hard or intermediate snow. In this respect, it is much like an ice skater who drives his or her blade into the ice to make a turn. A flexible blade would detract from the skater making a turn, just as a very soft ski in the section directly below the boot would detract from the skier turning in hard snow.
Some expert skiers performing giant slalom or super giant slalom have found that their turning ability is enhanced when they attach to the ski, such as by gluing, a thin plate on top of the ski in the binding area. This added plate increases the distance between the skier's boot and the edges of the ski, and enhances the leverage which the skier has to drive the edges of the ski into the snow. WIPO Document 83/00039 discloses a device wherein glue and an elastomeric material hold a plate for supporting a toe piece and heel piece to the ski. The elastomeric material absorbs some of the vibration of the ski on the hard snow and relieves some of the discomforting noise of the ski rapidly smacking against the snow. Furthermore, the device stiffens the ski/plate/binding combination in the underfoot area of the ski improving edge control on hard snow. In another device called the Rossi-Bar and disclosed in European Patent Office Publication No. 0409749, a support bar on the ski has stops of elastomeric material at its forward and rearward ends. However, the bar is locked to the ski by clamps along the length of the bar, and it is the clamps and not the rubber stops which prevent the bar from sliding on the ski. Thus, the plate reduces the bending of the ski. In U.S. Pat. No. 3,937,481 mentioned earlier, a ski binding having an elongated plate is slidably mounted thereon for cushioning the skier when a forward abutment is encountered. Only the forward or toe portion of the system is fixed to the ski, so that the plate allegedly follows the bending of the ski. The device in fact impedes the bending of the ski since it is strapped to the ski in a number of places. A similar device with similar shortcomings is disclosed in Austrian Patent 373,786. A device of this type is sold under the name Derbyflex. It has been believed by many experts that raising the ski binding with such a plate detracts from the skier's ability to control the ski, since it was thought that the skier had to be close to the snow to "feel" the snow and ski accordingly. The present inventors and other manufacturers believe that this notion is wrong for most types of skiers, and that holding a ski boot somewhat high over the ski increases his or her ability to control the ski. Other patents disclosing ski bindings for increasing stiffness in skis include German Patent 2,135,450 and European Publication 0409749A1.
Even though the added plate is beneficial, it only applies to skiing on hard snow where a stiffer underfoot ski is desirable. When used on softer or powder snow, the added stiffness detracts from the skier's ability to control the ski since easier bending adds to the turnability of the ski in soft snow.
Other devices are known having movable boot support plates on skis. For example, U.S. Pat. No. 4,974,867 discloses a shock absorbing buffer disposed between a ski and a binding, and is not really related to the stiffness of the binding.
The skill of the skier is another condition which the skiing apparatus should take into consideration. Although stiff skis are beneficial to good skiers in events such as giant slalom and super giant slalom, novice skiers should generally use flexible skis for all events, since they enable reasonable performance even though edge control in turns may be sacrificed.
The skis are generally desired to have a greater degree of flexibility when they are travelling down the fall line of a slope, and to be stiffer when they enter into and continue a turn. Skis heretofore have generally been incapable of changing their flex as they move into or out of a turn.
The inventors are unaware of any ski bindings or skis which are adaptable to vary the stiffness or change the vibration characteristics as skis enter a turn, continue a turn, or exit from a turn.